Such lasers are within the category of molecular lasers. They operate almost always continuously. Despite the fact that CO.sub.2 has given them their name, other substances, such as, for example, N.sub.2 are represented in substantially higher percentages. The mixture of gases may consist, for example, of 10% CO.sub.2, 20% N.sub.2 and 70% He.
At around 15%, the efficiency of the CO.sub.2 laser is relatively high. Its wavelength is around 10.6 micrometers and is thus in an atmospheric "window". In consequence, it can also be guided over considerable distances in the atmosphere with minimal damping. If it is desired to use the laser beam to cut through relatively thick metal plate, then with the current state of the art, cutting must be carried out in an oxygen atmosphere, because lasers which are not subsidized, but which are sold industrially at a profit, only give off energy continuously in a kilowatt range.
Vital to the quality of cutting is the distribution of the laser beam energy over its cross-section. Truly ideal is the mode of zeroth order, also referred to as the Gaussian mode and characterized by a very homogeneous Gaussian distribution. This mode also imitates the peripheral form of a machine tool, such as for example, a drill, a milling tool, a nibbler or the like, so that not so very much cogitation is required in this respect.
Laser beams can be deflected, of course, by mirror movements and so create patterns on the material which is to be machined, or they may, of course, pass completely through the material. Here, too, it is possible to work more easily with the circular beam because the reflection of a circle is more easily monitored than the reflection of complicated figures.
For equal energy, the mode of zeroth order also has a smaller cross-section than modes of a higher order. This means for instance that it is possible for the mirrors, too, to be made smaller. Also, it is easier to forecast how a mirror surface will behave when reflecting a mode of zeroth order.
Whether a mode of zeroth orderis approximately or entirely achieved depends less upon the constancy of interval between the mirrors participating in the resonance. Instance, the essential criterion here is the deviation of the mirror reflection from parallelity in relation to the geometrical longitudinal axis of the laser. This deviation may have several sources. Naturally, manufacturing faults play a part. Another contributing factor is whether such lasers have a length which falls in the meter range. Here, the statically produced sag caused by the earth's attraction may play a part. Machine tools are also subject to all manner of vibrations of the most widely diverse amplitude and frequency whether they are generated by the machine tool which is equipped with the laser or whether they are caused by other machinery, vehicles, lifts or the like. In those cases, too, there are deviations from the ideal mode. Above all, though, the energy wasted gives rise to deviations of curvature from the geometrical longitudinal axis. This is due to the following consideration which is based on magnitude: let us assume that the electrical energy supplied to a laser is 3 kilowatts. The laser beam emitted is assumed then to have an effective output of 500 Watts. The energy irradiated is then, in terms of magnitude, around 2.5 kilowatts. If a laser is switched on when work commences, then the mode may initially be correct. With increasing heating-up of the mechanical supporting device, the mode tends increasingly towards a mode of higher order which may perhaps not be noted, if at all.
A disadvantage of current lasers is, too, the fact that their energy cannot be multiplied while retaining essential structural principles. Each laser is a specialist in its own field.